This invention relates to a method for producing flame retardant cellulosic materials and more particularly to a method for producing a flame retardant particle board.
Cellulosic materials such as paper, wood, cotton and the like are commonly used for household and commercial applications. Such materials are highly flammable and when ignited the fire spreads rapidly. Nevertheless, such materials are commonly used. Accordingly, a number of methods for treating such materials to reduce their flammability have been developed. However, such methods may be inadequate for today""s standards, may prove too costly for the commercial market, provide too little protection against fire and smoke and result in products with other shortcomings.
The use of cellulosic products which are treated with fire retardant materials frequently involve human beings, who incorporate such products in a confined space as for example in a home, kitchen or other room. Therefore the products must provide a safe environment and at the same time provide a pleasing appearance particularly when the products are made of particle board. Therefore the use of volatile or harmful solvents should be minimized and preferably avoided.
It is also important to eliminate volatile or harmful solvents which could cause problems during a process for treating cellulosic material with a flame retardant agent. Further, it is important that any treatment minimizes the likelihood of chemical exuding from the processed material. It is also important that any chemical treatment should not produce or release toxic substances onto the surface of a product.
Conventional methods for treating cellulosic materials such as particle board and the like typically include the application of salts of phosphoric acid, boric acid etc. Other methods use various organic solvent systems. Both of such methods may be economical, but often result in crystallization of salts on the surface of a wood product. In addition, such methods may result in migration of undesirable chemicals to the surface of products made thereby. The solvents used are often volatile during the application of the flame retardants and exude from the finished products.
It has also been recognized that ammonium phosphates are among the more effective inorganic fire retardants which are commonly used to treat cellulosic materials. Such phosphates are typically present as diammonium phosphate, monoammonium phosphate or simple or complex mixtures of such phosphates. Fire retardants of this type are prepared by reacting aqueous phosphorous acid with an alkaline oxide such as ethylene oxide.
A more recent approach to provide a non-blooming fire retardant composition is disclosed in the U.S. Pat. No. 4,539,045 of Wagner. As disclosed therein, an ammonium phosphate-containing fire retardant includes an effective amount of boric acid or alkali metal borate. The ammonium phosphate-containing fire retardant comprises a reaction mixture of aqueous phosphoric acid and an alkylene oxide. Boric acid or alkali metal borate is present in an amount of from about 2.5 to about 12 percent by weight of solids.
It is now believed that there may be a large commercial demand for an improved fire retardant cellulosic products in accordance with the present invention. It is believed that this demand extends to a fire retardant particle board which has improved heat and flame resistance. A demand for an improved fire retardant cellulosic material is further supported by the products"" enhanced properties. For example, such products do not include toxic substances and produce minimal smoke when exposed to heat and/or open flame. Accordingly, there is no harmful vapor or toxic substance to deal with during the manufacturing process.
In addition, products in accordance with the present invention do not exude toxic substances during or after manufacture or when exposed to high temperatures and/or open flame. Further the chemicals incorporated do not migrate to the surfaces or result in unsightly blemishes. Finally it is believed that the products as disclosed herein can be manufactured in a cost effective manner and brought to market at a competitive price.
In essence, the present invention contemplates a method for producing flame resistant or fire retardant cellulosic materials and more particularly to a method for producing a fire retardant particle board with improved resistance to flame and heat. The method includes the step of providing an aqueous solution of monoammonium phosphate and diammonium phosphate. The solution contains between about 0.325 and about 1.0 moles per liter of monoammonium phosphate and between about 0.325 and 1.0 moles per liter of diammonium phosphate. A metal hydroxide, preferably aluminum hydroxide, is added to the aqueous solution in an amount of between about 0.325 and 1.0 moles per liter to thereby provide a modified solution.
The method also includes the step of providing a mass of cellulosic material, preferably wood chips or fibers of the type used in producing a conventional particle board. About 450 to about 550 grams and preferably about 500 grams of cellulosic material per liter is added to the previously mentioned solution. After adding the cellulosic material to the modified solution, the mix is stirred or agitated until the cellulosic material is thoroughly saturated. In practice vigorous stirring, i.e. a conventional stirrer at medium speed, is continued until the mix forms a uniform dark brown color. To ensure thorough saturation, the stirring or other agitation may continue for about one minute after the uniform dark color is reached.
The mix is then dried in a conventional manner at a temperature of between about 105xc2x0 C. to about 120xc2x0 C. The higher temperatures provide more rapid drying, but care should be used to avoid overheating or carbonizing the heated material.
The method also includes the step of providing a powdered glue which is selected from the group of urea formaldehyde resin, phenolic resin or mixtures thereof. In a preferred embodiment of the invention, the powdered glue is dissolved in water and then mixed with an aqueous solution of diammonium phosphate and monoammonium phosphate for a period of 10 to 15 minutes. The treated glue should contain between about 54 to about 66 percent by weight water, between about 33 to about 39 percent by weight glue, between about 1.5 and about 2.5 weight percent monoammonium phosphate and between about 1.5 and 2.5 weight percent diammonium phosphate.
The dried saturated cellulosic material is then mixed with the modified glue composition.
Finally the pulverized mass is formed into a mat and placed on a suitable press where it is subjected to heat and pressure to consolidate the particles and thereby form a particle board with enhanced heat and flame resistance.
The invention will now be described in connection with the accompanying drawings.